How much concrete do I need?

Calculate the volume: length × width × thickness. For example, a 3×3 m slab at 10 cm thick = 0.9 m³ of concrete. The calculator also converts this into the number of bags.

How many bags of concrete per cubic metre?

One 25 kg bag of dry-mix concrete yields about 12 litres of finished concrete, so a cubic metre (1,000 l) takes about 80–85 bags. For large pours, ready-mix concrete is more practical.

When should I order ready-mix concrete?

For pours over 1 m³, ordering ready-mix concrete from a truck is often cheaper and easier than mixing bags by hand. For small jobs, bagged concrete is enough.

How much does concrete weigh?

The density of concrete is about 2,400 kg/m³, i.e. 2.4 tonnes per cubic metre. This is worth keeping in mind, for example, when planning load-bearing structures and transport.

Concrete Calculator — Bags Needed

Calculate how much concrete or ready-mix bags you need for a pour. Footings, floors and posts. Free concrete calculator.

Length: 3.00 m

Width: 3.00 m

Thickness: 10 cm

Bag size: 25 kg bag

0.90 m³

Concrete needed

Volume	0.90 m³
Concrete (kg, ~2400 kg/m³)	2,160 kg
Bags needed	87 bags

ℹ️ The density of concrete is about 2400 kg/m³. One 25 kg bag of ready-mix concrete yields about 12 litres (0.012 m³) of finished concrete. For large pours (over 1 m³) it is worth ordering ready-mix concrete by truck — it is cheaper.

The concrete calculator tells you how many cubic metres of concrete your pour needs and how many ready-mix bags to buy. Enter the dimensions to get the volume, the weight in kilograms and the number of bags for footings, slabs or columns.

How the calculator works and what it’s for▾

How the volume is calculated

The amount of concrete is the length multiplied by the width and the thickness. Because thickness is given in centimetres while the other dimensions are in metres, the calculator converts the units for you.

For example, a footing 4 m long, 0.5 m wide and 20 cm thick is 4 × 0.5 × 0.20 = 0.4 m³ of concrete.

What you enter and what you get

You give the length and width in metres, the thickness in centimetres and the bag size you plan to use. The result shows the volume in cubic metres, the estimated weight in kilograms and the number of bags required.

The weight estimate is based on a concrete density of roughly 2400 kg/m³.

Bags or delivered ready-mix

One 25 kg bag of ready-mix yields about 12 litres, or 0.012 m³, of finished concrete. For small jobs such as post bases or small slabs, bags are convenient.

For pours over one cubic metre it is usually cheaper to order delivered ready-mix by truck, which also saves the mixing work.